A (direct-current to direct-current) DC to DC converter can include a controller to generate a pulse-width modulation (PWM) signal to drive a switching circuit, so as to control an output voltage of the DC to DC converter. For example, the controller can increase the output voltage by increasing the duty cycle of the PWM signal, or decrease the output voltage by decreasing the duty cycle of the PWM signal.
A conventional controller 150 for the DC to DC converter is illustrated in FIG. 1A. The controller 150 includes an oscillator 152, a comparator 154, an operational transconductance amplifier (OTA) 156, and a capacitor 158. The oscillator 152 provides an oscillating voltage 160 to a non-inverting input terminal of the comparator 154. A reference voltage 162 on the capacitor 158 is provided to an inverting input terminal of the comparator 154. The comparator 154 compares the oscillating voltage 160 with the reference voltage 162 and outputs a PWM signal 168 according to the comparison. The reference voltage 162 is within a range between a maximum level and a minimum level of the oscillating voltage 160. If the reference voltage 162 increases, the duty cycle of the PWM signal 168 decreases, and thus the output voltage of the DC to DC converter decreases. If the reference voltage 162 decreases, the duty cycle of the PWM signal 168 increases, and thus the output voltage increases.
The OTA 156 receives a predetermined voltage 166 and a feedback voltage 164 indicative of the output voltage of the DC to DC converter, and provides a control current ICOMP proportional to the difference between the predetermined voltage 166 and the feedback voltage 164. The output terminal of the OTA 156 is coupled to the capacitor 158, such that the control current ICOMP can control the reference voltage 162 on the capacitor 158. For example, if the feedback voltage 164 is greater than the predetermined voltage 166, the OTA 156 can output the control current ICOMP to charge the capacitor 158 in order to increase the reference voltage 162. Thus, the output voltage decreases. If the feedback voltage 164 is less than the predetermined voltage 166, the OTA 156 can absorb the control current ICOMP from the capacitor 158 in order to reduce the reference voltage 162. Thus, the output voltage can increase. As a result, the output voltage of the DC to DC converter can be adjusted to a desired level determined by the predetermined voltage 166.
However, in the conventional controller 150, the power consumption of the oscillator 152 can be relatively high. In addition, the capacitor 158 may not be integrated together with the comparator 154 and the OTA 156 into a single chip because of the large size of the capacitor 158. Furthermore, the bandwidth of the OTA 156 may be too narrow that the response time of the OTA 156 is delayed. Therefore, the controller 150 may not control the output voltage accurately.